Pogba came off towards the end of United’s 2-0 win at Burnley last weekend with a hamstring complaint and has not recovered in time for the clash at City.
Asked if Pogba was fit, Mourinho said: “Paul? No.”
The loss of Pogba is a huge blow for United and means Mourinho is missing six players, with Phil Jones, Chris Smalling, Juan Mata, Marcos Rojo and Zlatan Ibrahimovic also ruled out through injury.
“I trust the boys and we go with everything we have, and we go until the last second of the season,” said Mourinho. “We are fighters, the boys are fighters and we go.”
United trail Pep Guardiola’s side by a point in a game that could ultimately determine which of the Manchester clubs secures a top-four spot and Champions League football next season.
Mourinho said it will mean nothing to United if they finish above City but do not secure Champions League football, either via a top-four finish or by winning the Europa League.
“It means nothing, it means nothing,” said Mourinho. “if you finish fifth and they they finish sixth, we’re above them, but it means nothing.
“If they finish third and we finish fourth, they’re above us and it means a lot. But this is not about Pep or City, it’s about objectives, and we want to play Champions League football and we still have two doors open.”
On leading scorer Ibrahimovic, whose season was prematurely ended by a cruciate ligament injury, which will rule him out for up to a year, Mourinho was positive on the 35-year-old’s chances of making a full recovery and playing again.
“The future is a big surgery, a long period of recovery, but the future is also in the end a very strong guy, mentally very very strong, one who wrote immediately on his social media he will stop when he wants, not when people think so,” said Mourinho.
“So it looks to me he’s not going to give up, he’s going to fight and I’m really pleased about that. He fought all his life since he was born, I don’t see a reason for him not to fight.”
Asked how the injury affected Ibrahimovic’s United future, with the striker out of contract this summer, Mourinho said: “I don’t know, I don’t want to know, I’m not interested in it, I don’t care about it, I just want the difficult surgery to go and we think he’s in fabulous hands and now he must recover from the injury and prepare himself mentally for the next step.
“I think the next step will be something he really wants, which is what I was saying before the injury in the period of doubts over his future. He’s much more important than me and what I want.
“I always want the players to be happy, to choose their future, but now, before such an important surgery, I think it’s a waste of time to speak about what next.”